Floating structure with rotatable templet for connecting guide lines thereto

ABSTRACT

A constant tension system for guide lines used in connecting an underwater wellhead to a dynamically stationed ship wherein twisting of the guidelines is prevented by mounting the guidelines on a rotatable templete disposed on the structure.

United States Patent 1191 Busking Sept. 25, 1973 1 FLOATING STRUCTUREWITH ROTATABLE TEMPLET FOR CONNECTING GUIDE LINES THERETO [75] Inventor:Bob E. Busking, The Hague,

Netherlands [73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: May 26, 1971 1211 Appl. No.: 147,110

[30] Foreign Application Priority Data June 29, 1970 Great Britain31,390/70 [52] U.S. C1. 166/.5, 114/.5 D [51] Int. Cl EZlb 7/12, E21b43/01 [58] Field of Search 166/.5, .6; 175/7, 175/5; 114/.5 D

[56] References Cited UNITED STATES PATENTS 3,191,201 6/1965 Richardsonet a1 114/.5 D 3,279,404 10/1966 Richardson 114/.5 D

3,481,294 12/1969 Vincent 175/7 3,602,302 8/1971 Kluth 166/.5 3,605,6689/1971 Morgan 175/7 Primary Examiner-Marvin A. Champion AssistantExaminerRichard E. Favreau Attorney-Theodore E. Bieber and Harold L.Denkler [5 7 ABSTRACT A constant tension system for guide lines used inconnecting an underwater wellhead to a dynamically stationed shipwherein twisting of the guidelines is prevented by mounting theguidelines on a rotatable templete disposed on the structure.

3 Claims, 1 Drawing Figure 4. r" 'CONTROL 1 2 76 TRANSDUCER I6TRANSDUCER Pmmmsm 3,760,875

42 CONTROL BEBusk/ng,

INVENTOR FLOATING sTRucTunEwrrn ROTATABLE TEMPLET FOR' CONNECTING eunmLINES THERETO 1 BACKGROUND OF THE INVENTION The invention relates to afloating structure which is suitable for carrying out well drilling,completion, workover and/or production operations. Since the structurehas to remain above the location where these operations are carried out,means are provided for maintaining the structure, such as a ship or afloating platform, at such location during the period that theseoperations are carried out. I

In particular, thepresent invention relates to a floating structureprovided with a dynamic stationing sysmm, which canbe applied withspecial advantage in deep waters where anchoring by means of anchors andanchor cables is not possible or attractive. Suchadynamicstationingsystem comprises measuring means for measuring thedisplacement of the floating platform from a desired location, and meansfor controlling propulsion units of the structure in such a manner thatthis displacement is kept as small as possible. Such a system .may, ifdesirable, further include measuring means for measuring the deviationof the floating platform from a desired heading, and means forcontrolling propulsion units of the structure in such a manner as tokeep this deviation as small as possible. It will be understood that insuch a system the forces for stationing the floating structure aresolely provided by the propulsion units of the floating structure, whichunits may include bow and/or stern propellers and/or propellers of theVoith Schneider type (also referred to as vertical blade "In a preferredmethod of operation, the desired heading corresponds to the directionfrom which the wind is blowing, and the floating structure is,notwithstanding the wave, wind and current forces acting on thestructure, kept at the desired location in the desired heading by thedynamic stationing system. It will be appreciated that a change in winddirection calls for a resetting of the desired heading, since, inparticular when the floating structure is a ship, such a change mayresult in an increase of the forces exerted by the wind on the ship.However, if the forces exerted on the structure by the water current aredominant, the desired heading will be set in relation to the prevailingwater current.

A floating structure as mentioned hereinabove for carrying out welldrilling, completion, workover and/or A drawback attached to the use ofthese lines or cables extending between the floating structure providedwith a dynamic stationing system and submerged well equipment is thatthe lines or cables are liable to become twisted and damaged owing tocontactwith the marine riser pipe by the movements of the structure, orthe re-setting of the desired heading.

BRIEF SUMMARY OF THE INVENTION The object of the present invention is toprevent such twisting and-damage of cables and/or lines extendingbetween underwater well equipment and a floating structure which isprovided with a dynamic stationing system.

According to the invention,a floating structure provided with a dynamicstationing system comprises a moonpool extending substantiallyvertically through the structure and suitable for passing equipmenttherethrough when carrying out well drilling, completion, workoverand/or production operations, a derrick mounted on the structure at alocation above the moonpool, a templet mounted around the moonpool,which templetis rotatable with respect to the floating structure and thederrick mounted thereon, and at least one constant tension devicemounted on the' templet, an elongated flexible means being coupled atone end thereof to the constant tension device, the other end of saidmeans being suitable for connection to underwater well equipment.

The elongated flexible means may be a guide line or a hose cable.

Means may be provided for rotating the rotatable templet.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF PREFERRED EMBODIMENTThe ship 1 floating in the sea'2 comprises a well or moonpool 3extending vertically through the body of the ship and suitablefor'passing drilling equipment as well as completion equipmenttherethrough. Above the moonpool 3 a derrick 4 is mounted on thedrilling floor 5, which in its turn is mounted on the deck 6 of the ship1 by means of columns 7. With the exception of the rotary table 8, allthe other equipment as used on the drilling floor 5 and in the derrick 4is not shown for sake of simplicity.

The templet 9 is mounted above the moonpool 3 and below the drillingfloor 5, in a rotatable manner around the central axis of the moonpool 3by means of the bearing elements 10.

The ship 1 is kept at the desired location above the well 11 penetratingthe sea bottom 12, by propulsion means of'which only one, being a VoithSchneider propeller l3 installed forward of the moonpool is shown.Acoustic transmitters 14 (of which only two are shown) are mounted onthe base member 15 of the well 11, and the acoustic signals generated bythe transmitters are received by the listening microphones 16 carried bythe ship 1 (only two microphones being shown in the drawing). Thesignals received by the micro- 4 phones are sent to a measuring andcontrol device 17,

in which the displacement from the desired location is measured andcontrol signals are generated for controlling the operation of the VoithSchneider propeller 13 as well as the operation of any other propulsionunit (not shown) which is used for stationing the ship 1. The controlsignals generated may include information obtained on the deviation ofthe ship from a desired heading. To this end, a compass 18 is providedsuitable for determining the magnitude of this deviation, which is thensupplied to the measuring and control device 17 and combined with theinformation on the displacement for generating control signals to besupplied to the propulsion units acting to keep the ship on the desiredlocation and on the desired heading.

In the dynamic stationing system as shown in the drawing, thetransmitters l4 operate on different frequencies and the time intervalsbetween the moments of arrival of the signals of a common frequency atthe receivers 16 are used for calculating the displacement of the shipfrom the desired location.

It will be appreciated that the dynamic stationing system asschematically shown in the drawing is only indicated by way of example.There are various other types of dynamic stationing systems which areknown per se and which may be used in a floating structure according tothe present invention.

The base member of the well 11 further carries guide posts 19 to. whichare connected guide lines 20 running upwards to the ship 1. The linesare connected to the drums 21 of constant tension winches 22 which aremounted on the rotatable templet 9. The guide lines 20 are used forguiding well equipment from the ship 1 to the well 11, such as thewellhead 23 which is provided with guide bars 24 co-operating with theguide lines 20, and the marine conductor 25 provided with guide bars 26near the lower end thereof. The guide bars are in contact with the guideposts 19 over the lower part of their track along the guide lines 20,thus exactly centering the well equipment on the entrance to the well11.

The upper part of the marine conductor 25 includes a telescopic section27 of which the upper part is carried by the drilling floor 5, thesection 27 allowing the length of the conductor 25 to be adapted to thevariations in distance between the drilling table 8 and the sea bottom28 resulting from the wave action.

At a level below the telescopic section 27, a rotatable bearingelement29 is arranged around the marine conductor 25. One side of the bearingelement is connected to the conductor 25. The other side of the bearingelement is supported by supporting cables 30. Each cable 30 is connectedat the other end thereof to a constant tension device 31 and guidedthereto via a sheave 32. The constant tension devices are each connectedto a column 7. Each device 31 comprises a high pressure pneumaticcylinder 33 mounted on the column 7, the cylinder having a piston withpiston rod 34 slidably arranged therein. Means (not shown) are providedfor maintaining a constant pressure within the cylinder space below thepiston. Each cable is guided over two sheave blocks, one block 35 beingmounted at the closed end of the cylinder 33, the other block 36 beingmounted on the free end of the piston rod 34. The end of each cable 30is connected to a point fixed with respect to the cylinder 33.

OPERATION OF PREFERRED EMBODIMENT The ship 1 is dynamically stationed ona desired heading and on a location vertically above the well 1 l, andthe cables 20 are arranged to form a guide for any equipment which is tobe displaced between the ship 1 and the well 11 and vice versa. Thewinches 22 are actuated to keep the tension in these cables 20substantially constant notwithstanding variations in distance betweenthe ship 1 and the sea bottom 28 due to wave action. The same applies tothe constant tension devices 31 which by means of the supporting cables30 maintain a substantially constant tension in the upper part of themarine conductor 25 independent of wave action.

When the desired heading of the ship 1 has been reset (e.g., aftershifting of the wind), the dynamic stationing system will keep theheading of the ship as close as possible to this new heading, whichmeans that the ship will be rotated with respect to the well over anangle corresponding -to the deviation between the old heading and thenew heading. To prevent twisting of the guide cables 20 and to preventthem from touching the marine riser pipe 25, the templet 9 together withthe constant tension devices 22 carried thereby is rotated through anangle equal to the deviation between the two headings. Thus the cables20 remain parallel to each other and to the marine conductor 25 and-willnot be twisted.

Since the supporting cables 30 are suspended from the sheaves 32 whichare mounted to the drilling floor 5, these cables will be displacedthrough an angle equal to the deviation between the old heading and thenew heading after re-setting the desired heading. As, however, the lowerends of these cables are connected to a part of the supporting element29 which is rotatably arranged with respect to the conductor 25, thecables 30 will remain in a common plane but move to a plane. differentfrom the plane in which they were originally positioned. The guidecables 20, however, always remain in the same plane.

It will be understood that the templet 9 is preferably rotated by meansof an electric motor 40 driving the templet through a gear arrangement41. The templet may also be rotated by hydraulic means which may actuatethe templet by means of a pinion co-operating with gear teeth arrangedaround the circumference of the circular templet.

The operation of the electric motor or the hydraulic system may becontrolled by a push button. However, a control system 42 may be appliedfor controlling the operation of the electric motor automatically suchthat the templet is kept in a desired position under all circumstances.This arrangement is particularly preferred when applying a dynamicpositioning system which controls only the displacement of the ship froma desired location, and not the deviation of the ship from a desiredheading.

It will be understood that the invention is not restricted to theparticular embodiment as shown in the drawing by way of example. Thus,the constant tension devices 22 as used for maintaining a substantiallyconstant tension on the guide cables 20 need not be winches, but may beof any other type suitable for the purpose, such as the type 31 asapplied for tensioning the cables 30. However, these constant tensiondevices 22 will always be mounted on the templet 9.

Since the lateral loads exerted on the templet by the guide cables 20are of onlysmall magnitude, no special measures have to be taken tosupport the templet 9 against lateral loading. The bearing elements 10may be of any type suitable for the purpose.

The number of guide cables may be more than two (as shown in thedrawing) or even one. Further, any other connection between the ship 1and the well 11 and formed by an elongated flexible means, such as ahose cable, may be protected against twisting with respect to othercables or to the marine conductor in the manner as described withreference to the cables 20. The hose cable as mentioned may be appliedfor communication purposes by passing hydraulic signals therethroughfrom the ship 1 to the equipment on the well 11.

Although the derrick 4 as applied is mounted in a fixed position on thedeck 6 of the ship during drilling, completion or workover operations,this derrick may be displaced with respect to the moonpool 3 betweensuch operations.

I claim as my invention:

1. An improvement in a floating structure provided with a dynamicstationing system, including a moonpool extending substantiallyvertically through the structure and suitable for passing equipmenttherethrough when carrying out well drilling, completion, workoverand/or production operations, a derrick mounted on the structure at alocation above the moonpool, and underwater wellhead equipment disposedon the floor of the body of water, said improvement comprising:

a templet mounted around the moonpool, said templet being rotatable withrespect to the floating structure and the derrick mounted thereon, atleast one constant tension device mounted on the templet, and 1 anelongated flexible hose cable being coupled at one end thereof to theconstant tension device, the other end of the hose cable being suitablefor connection to the underwater well equipment.

2. A floating structure according to claim 1, and in addition a marineconductor extending from the floating structure to the wellhead, asupporting cable which is connected at one end thereof to a rotatablebearing element suitable for being connected to said marine conductor,and connected at the other end to a constant tension device which ismounted on a part of the structure which is stationary with respect tothe templet.

3. A floating structure according to claim 1 and in addition drive meansfor rotating the rotatable templet, measuring means for measuring thedeviation of the structure with respect to a predetermined heading andfor controlling the drive means for so rotating the rotatable templetthat the deviation of the templet with respect to the predeterminedheading is as small as possible.

1. An improvement in a floating structure provided with a dynamicstationing system, including a moonpool extending substantiallyvertically through the structure and suitable for passing equipmenttherethrough when carrying out well drilling, completion, workoverand/or production operations, a derrick mounted on the structure at alocation above the moonpool, and underwater wellhead equipment disposedon the floor of the body of water, said improvement comprising: atemplet mounted around the moonpool, said templet being rotatable withrespect to the floating structure and the derrick mounted thereon, atleast one constant tension device mounted on the templet, and anelongated flexible hose cable being coupled at one end thereof to theconstant tension device, the other end of the hose cable being suitablefor connection to the underwater well equipment.
 2. A floating structureaccording to claim 1, and in addition A marine conductor extending fromthe floating structure to the wellhead, a supporting cable which isconnected at one end thereof to a rotatable bearing element suitable forbeing connected to said marine conductor, and connected at the other endto a constant tension device which is mounted on a part of the structurewhich is stationary with respect to the templet.
 3. A floating structureaccording to claim 1 and in addition drive means for rotating therotatable templet, measuring means for measuring the deviation of thestructure with respect to a predetermined heading and for controllingthe drive means for so rotating the rotatable templet that the deviationof the templet with respect to the predetermined heading is as small aspossible.